Question about ISO, Sensor & Aperture

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steele_uk

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Andy
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I have a Canon 40D and have recently been slightly dissapointed in the noise i seem to experience at ISO 400 and above.

I am trying to get my head round whether i am expecting too much from this camera. I take a lot of indoor low-ish light without flash mainly people pics,

just wondering if you can help me with my understanding of the following;

I have been buying fairly fast lenses, such as the F/1.8 Canon 85MM and the Tamron 28-75 F2.8. to help with low light.

I didn't realise that a ISO400 would introduce so much noise, is this down to the 1.6 Crop Sensor, or is it due to some other internal processing?

I have seen wedding pics taken with D3, D700 at very high ISO 1000+ and didnt notice anything like the noise i experience.


So my real question is; Are you better off, getting a body capable of fantastic low noise/high iso performance, and don't worry quite so much about the speed of the lens you buy?


Please correct any of my statements,this is all new and i am still learning and getting to grips with all the theory.
 
Essentially you need a body with better high ISO performance like the Nikons you mentioned or the Canon 5d Mark II.

All a fast lens will do is give you the extra stop(s) to allow you to reduce the ISO. They won't effect the level of noise. The camera body will.
 
Im surprised your not happy with the noise at ISO 400 though, i would have thought the 40d can go a fair bit higher than that quite happily.

The D3 & D700 are a few steps up from the 40d i performance and price hence the better high ISO the same for the 5d2 and 1d3/4 from Canon.
 
Yep surprised as well. On my old 400D I was happy with performance up to ISO 800.

BUT ONLY if I keep the post processing to a minimum. Are you doing much to the image after capture?
 
Can you post an image or two so we can see what may be happening - I bet the images are under-exposed (don't take this as a criticism! :) )and this will cause a lot of noise to be present.
 
Thanks for the replies.

@Ninetyeight - I would say you are right, my images tend to err on underexposed. This tends to be as a result of me wanting to keep the iso low, no flash, and not got to the far extremes of a large aperture.

Do you mean that noise is present on an underexposed image due to the fact that it will have to have post processing work done to increase the exposure, or is there a more basic reason that an underexposed image will have noise?
 
It is better to raise the ISO and overexpose than to underexpose at any ISO. You will get more noise at ISO 100 if you underexpose it and then bring it back in PP than you will if you overexpose at ISO 400 and bring that back in PP

Underexposure is bad for noise control!
 
steele_uk said:
Thanks for the replies.

@Ninetyeight - I would say you are right, my images tend to err on underexposed. This tends to be as a result of me wanting to keep the iso low, no flash, and not got to the far extremes of a large aperture.

Do you mean that noise is present on an underexposed im age due to the fact that it will have to have post processing work done to increase the exposure, or is there a more basic reason that an underexposed image will have noise?
Click to expand...

The noise is introduced by the amplification necessary to raise the very small signal from the photodiodes to a level capable of being stored by the memory cards.

Since dark areas require higher magnification than light areas this introduces more noise in those areas.
 
Thank you, i am quite relieved to think that it may simply be my poor technique.:)
 
Give NeatImage trial a whizz.
I've found it can work wonders.
NoiseNinja is pretty good too.

Note: Both bits of software work best on an untweaked image, so it can apply the same algorithm and settings across the whole image.
 
steele_uk said:
Do you mean that noise is present on an underexposed image due to the fact that it will have to have post processing work done to increase the exposure,
Click to expand...

Exactly that :thumbs:

A lot of instructors actually recommend 'exposing to the right', overexposing (without blowing detail in the highlights) and then bringing back in PP.

Whatever, if you can get the image about right at 400-800 ISO you should notice an improvement :)
 
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